1. Field of the Invention
The present invention relates to a regulator circuit for adjusting an output voltage to predetermined DC voltage and maintaining thereat. More specifically, it relates to a DC regulator circuit for charging a battery which is to be connected to an output terminal and for applying predetermined DC voltage to a load.
2. Description of Related Art
MPU, LSI, IC used in various electric appliances, other semiconductor devices, drive motors such as HDD, FDD, and the like work using DC voltages of DC 5V, 3.3V and the like as their power source. Therefore, electric appliances as such need a DC/DC converter for converting a current voltage converted from AC 100V or the like via an AC adapter into a desirable current voltage value. Furthermore, as system gets further complicated, there may be some cases that various kinds of power source system may be needed and that an output voltage from a DC/DC converter is further converted by another DC/DC converter. Taking conversion voltage difference, required power source capacity and accuracy, and the like into consideration, these DC/DC converters are constituted by switching regulators or series regulators, in general.
In recent years, there have been some cases that, instead of an AC adapter, rechargeable batteries as DC power source are used for portable electric appliances such as note-type personal computers and cellular phones. In the above system, an electric appliance is connected to an AC adapter and the like for recharging operation. For controlling flow of charging current to a battery, battery voltage in a fully charged state and the like, a charging control device is provided for the portable electric appliances.
FIG. 13 shows a conventional charging control device 100. In the charging control device 100, switching control of a PMOS driver Tr1 is conducted. Thereby, a coil L1 and a capacitor C1 smooth out DC voltage outputted from an AC adapter 102 and the smoothed DC voltage is charged to a battery 101 via a charging current detecting resistance RS1. A diode D1 is a fly-back diode for regenerating charging current ICHG.
Switching control of the PMOS driver Tr1 is conducted by a charging control circuit 111. An amplifier 112 amplifies terminal voltage of the charging current detecting resistance RS1. An error amplifier 116 amplifies voltage difference between reference voltage V1 and the amplified terminal voltage of the charging current detecting resistance RS1 as error amplification, as well as outputs control voltage for constant current charging. Furthermore, resistance elements R110 and R120 divide output voltage VO at a charging-control-device output terminal VO that is a battery-side terminal of the charging current detecting resistance RS1. An error amplifier 118 amplifies electrical potential difference between reference voltage V2 at a reference-voltage terminal V2 and the divided voltage of the output voltage VO as error amplification, as well as outputs control voltage for constant voltage charging. The above two kinds of control voltage are inputted to a comparator 120 and compared with an oscillating signal from an oscillator (OSC) 122 there. Thereby, a switching duty is determined. In case control voltage for constant current charging derived from the error amplifier 116 determines a switching duty, constant current charging is controlled and charging current ICHG for the battery 101 is adjusted to a predetermined value of charging current ICHGM. In case control voltage for constant voltage charging derived from the error amplifier 118 determines a switching duty, constant voltage charging is controlled and the output voltage VO is kept at a predetermined value of full charging voltage VBAT0 so as to carry out charging.
According to a charging control method of the charging control circuit 111 shown in FIG. 13, the error amplifier 116 controls charging current ICHG for the battery 101 until charging begins and a value of output voltage VO at the charging-control-device output terminal VO reaches full charging voltage VBAT0. Thereby, charging is carried out rapidly with a predetermined value of charging current ICHGM. When charging to the battery 101 further goes on and the output voltage VO at the charging-control-device output terminal VO reaches full charging voltage VBAT0, a value of control voltage for constant current charging outputted from the error amplifier 116 and that for constant voltage charging from the error amplifier 118 reverse. As a result, charging control is switched from constant current control to constant voltage control. Charging operation further goes on with the output voltage VO at the charging-control-device output terminal VO kept at full charging voltage VBAT0. Charging to the battery 101 completes when the charging current ICHG decreases from its predetermined charging current ICHGM and finally runs out.
Since the charging control device 100 and the battery 101 are connected via connectors, switches and the like, there are resistance elements such as contact resistances and the like at connecting portions of the connectors and the like. A wiring resistance of connection wiring itself is also arranged together with the contact resistance at a connecting portion and a parasitic resistance RLS1 is inserted at a connecting path. Since charging current ICHG flows in the battery 101 through the parasitic resistance RLS1, voltage drop xcex94VLS occurs when charging current ICHGM in a constant current control state flows. As a result, battery terminal voltage VBAT lowers by the voltage drop xcex94VLS, compared with output voltage VO at the charging-control-device output terminal VO. The charging control device 100 carries out constant voltage control with respect to output voltage VO at the charging-control-device output terminal VO. Therefore, as constant current charging control further goes on and battery terminal voltage VBAT gets higher, output voltage VO at the charging-control-device output terminal VO gets higher. And then, at a point where the charging-control-device output terminal VO reaches full charging voltage VBAT0, output charging control is switched from constant current control to constant voltage control.
However, the battery terminal voltage VBAT does not reach full charging voltage VBAT0 of the battery 101 at this point but is charged up to voltage level lowered by voltage drop xcex94VLS from the full charging voltage VBAT0. That is, constant charging control is supposed to conduct high-speed charging control primarily, however, the voltage drop xcex94VLS due to the parasitic resistance RLS1 shortens constant charging control time. Along with that, it takes long to fully charge the battery 101, which is problematic.
FIG. 14 shows the battery charging characteristics of the conventional regulator circuit 100. In the regulator circuit 100, charging current ICHGM flows to the parasitic resistance RLS1 during the constant current control period. Thereby, output voltage VO of the charging-control-device output terminal VO has a voltage value higher by the voltage drop xcex94VLS compared with battery terminal voltage VBAT. Consequently, before the battery terminal voltage VBAT reaches a value of predetermined voltage VBAT0 in a full-charging condition, the charging control manner is switched from constant current charging control to constant voltage charging control. As a result, a constant current charging control period gets shorter than original one. Subsequent charging control is made in accordance with constant voltage charging control and the battery terminal voltage VBAT is further charged by the drop voltage xcex94VLS. However, the constant voltage charging control is conducted in a manner that charging-control-device output terminal VO which has already reached full charging voltage VBAT0 is kept at voltage VBAT0. Therefore, a switching duty of the PMOS driver Tr1 must be lowered inevitably. Accordingly, the charging current ICHG of the related art lowers in a short charging period compared with ideal charging current ICGH_I. Consequently, the battery voltage VBAT takes a long charging time to reach full charging voltage VBAT0 compared with ideal battery voltage VBAT_I. That is, there is required a full charging time tx longer than a full charging time t0 taken in case original constant current charging control is conducted.
Furthermore, it is possible to avoid influence of voltage drop xcex94VLS due to the above-mentioned parasitic resistance RLS1 by a manner such that full charging voltage under a constant voltage control condition is set to a sum of full charging voltage VBAT0, suitable to a specification of the battery 101, and voltage corresponding to voltage drop xcex94VLS. However, in this case, battery terminal voltage VBAT in a full charging condition gets higher than the voltage suitable to the specification of the battery 101. This causes huge voltage stress to the battery 101 and affects battery performance, which is problematic.
Furthermore, constant current control may be utilized for current limitating control so that the charging control circuit 111 can be used as a regulator circuit for supplying constant voltage to loads. Even in this case, a parasitic resistance RLS exists between the output terminal VO and a load. Therefore, voltage applied to the load lowers by drop voltage xcex94VLS from a predetermined voltage in a large load current region reaching an over-loaded state. This makes it impossible to apply predetermined voltage to a load accurately in the entire load current region, which is problematic.
The present invention, attempted to resolve the above-noted problems with the prior art, is intended to provide a regulator circuit capable of accurately adjusting and maintaining output voltage in any points of charging current region and load current region by correcting setting of predetermined voltage to be regulated depending on values of charging current and load current.
In order to achieve the above-stated object, there is provided a regulator circuit directed to one aspect of the present invention comprising: an output voltage control section for controlling output voltage based on reference voltage; an output current detecting section; and a reference voltage correcting section for controlling the reference voltage based on output current detected at the output current detecting section.
In the regulator circuit directed to the one aspect of the present invention, the output voltage control section controls output voltage using reference voltage controlled by the reference voltage correcting section, based on output current detected at the output current detecting section.
Thereby, output current flows through a parasitic load element on a current path. Even if voltage values of output voltages on the current path, potential values of which should be equal essentially, are not same, the reference voltage correcting section controls a value of the reference voltage depending on a value of the output current. Accordingly, output voltage at a predetermined position on the current path can be adjusted appropriately. Even if there is a distance between a position where the output voltage control section should control output voltage depending on a value of the reference voltage and a position from which a controlled output voltage is desired to be taken, on the current path, a desired value of output voltage can be obtained.
Furthermore, the regulator circuit directed to the one aspect of the present invention may further include an output current control section for controlling output current based on a detection result obtained by the output current detecting section. Thereby, output voltage can be controlled depending on a value of the output current and the output current can be controlled, as well.
There is provided a regulator circuit controlling method of making reference voltage variable which is directed to the one aspect of the present invention, the reference voltage adjusting output voltage to predetermined voltage and maintaining thereat depending on a value of output current.
Thereby, output current flows through a parasitic load element on a current path. Even if voltage values of output voltages on the current path, potential values of which should be equal essentially, are not same, the reference voltage can be variable depending on a value of the output current. Accordingly, output voltage at a predetermined position on the current path can be adjusted appropriately and kept at an appropriate value. Even if there is a distance between a position where the output voltage control section should control output voltage depending on a value of the reference voltage and a position from which a controlled output voltage is desired to be taken, on the current path, a desired value of output voltage can be obtained.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in conjunction with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention.